The present invention relates generally to a novel suspension system for the rotor component in a rotor/stator assembly, and more particularly to such a system which provides for passive and stable suspension of the rotor within a fluid pump. Assemblies utilizing the features of the present invention are adapted for a wide variety of applications, including fluid handling systems for fragile or aggressive fluids, as well as applications for such assemblies which may be characterized as either delicate and/or rugged. The novel passive and stable suspension system of the present invention includes a rotor which is typically suspended within a stator, with the rotor being stabilized through passive magnetic as well as hydrodynamic forces.
The magnetic components may be designed in a variety of different coupling arrangements, with passive magnetic bearings being employed for creating stability along certain selected planes or axes and further creating one resultant unstable negative force in one plane or along an axis. More specifically, the magnetic forces are designed to create an unstable negative force in a plane perpendicular to the axis of rotation of the rotor, with stable and positive forces and moments being created in all other degrees of freedom excepting of course, rotation of the rotor. This resultant instability in the plane perpendicular to the axis of rotation is overcome upon rotation of the rotor creating a centrifugal force of magnitude greater than that of the unstable negative force. In other words, when rotating, the forces created in the rotor return the body to an appropriate point of origin for the intersection of the X, Y and Z axes. Here, the positive forces and moments are defined as forces and moments applied to the rotor in the direction of the origin, and, correspondingly, negative forces and moments apply to the rotor in directions away from the origin.
The suspension system of the present invention utilizes magnetic bearings for creation of positive stiffness and a resultant negative stiffness, with the overall stiffness in five of the six degrees of freedom being positive. Dynamic stability of the system is ultimately achieved through centrifugal/centripital forces, with dynamic stability being achieved.
Except for the passive magnetic stabilization system and the dynamic magnetic forces utilized to drive the rotor, the fluid pumps of the present invention are otherwise bearing and seal-free. Passive magnetic forces are applied to the rotor during periods of rotation and dwell, with these passive forces including a resultant unstable negative force in a plane or along an axis perpendicular to the axis of rotation. As such, fluid pumps employing the magnetically stabilized rotor/stator assemblies of the present invention are particularly well adapted for a wide variety of mechanical applications, with one such application being in a centrifugal pump for handling highly aggressive materials such as corrosive, poisonous, or dangerously radioactive fluids, as well as fragile fluids including human or animal blood. Another pump application is an axial pump. The impeller in centrifugal pumps transfers the kinetic energy to the fluid by blades/vanes disposed thereon, or by surfaces based on Tesla principles. Such surfaces may include, for example, parallel or non-parallel disks or cones radially arranged about and extending from the rotor axis. During any transfer/movement of such fluids, it is frequently dangerous to expose the fluids to forces such as unusual impact and/or shear forces, and thus the advantage of utilizing bearing and seal-free pumps, and particularly one wherein the rotor/stator assembly is at least partially magnetically stabilized.
A particularly advantageous feature of the present invention is that of providing a passive magnetic force to the rotor which when combined with centrifugal forces created in rotation of the rotor in fluid, reduces and/or completely eliminates surface-to-surface contact between rotor and stator surfaces. Elimination of the surface-to-surface contact between the rotor and stator prevents undesired frictional heat input, as well as premature wearing of the respective components of the fluid pump. An additional aspect of the passive magnetic suspension combined with such centrifugal forces is in the fact that the clearance between the rotor and the stator is not a critical dimension with respect to the maintenance of a properly suspended rotor within the stator. Therefore, fluid pumps having relatively larger clearances between the rotor and stator are made possible by the suspension system of the present invention. Such larger clearances accordingly reduce shear forces that can be damaging to fragile fluids. In fact, the clearances between the rotor and the housing in fluid pumps of the present invention are sufficiently large so as to negate boundary layer pressure effects and fluid shear stresses under the Prandl theory that are commonly referred to as “hydrodynamic bearings”. Accordingly, rotors utilized in the present invention do not rely upon such hydrodynamic bearings to remain properly positioned within the pump housing, but rather are positionably stabilized through the combination of passive magnetic bearings and centrifugal forces generated in operable rotation of the rotor.
In connection with one application of the present invention, pump assemblies utilizing the features of the present invention may be exposed to aggressive fluids, including corrosive, poisonous or radioactive fluids, as well as fluids which cannot tolerate contamination. Through elimination of seals and/or bearings, the lifetime and/or longevity of the pump is substantially increased.
Poisonous fluids, for example, become extremely dangerous whenever leakage develops, a common consequence of bearing and seal failure. In fluid pumps in accordance with the present invention, a rotor or impeller is utilized in an assembly which is bearing and seal-free, with the rotor being dynamically balanced and stable during operation. Bearing and seal-free pumps utilizing the rotor/stator assemblies of the present invention are particularly well adapted for transferring human blood and other delicate liquids without damaging and/or otherwise significantly adversely affecting their composition or quality. Furthermore, the magnetic stabilization feature of the present invention provides stable positioning of the rotor during operation. The passively suspended rotor is preferably operably positioned within the stator independent of forces external to the fluid pump. Depending upon the application, the rotor may be fabricated from any of a variety of non-magnetic materials, including, for example, metals such as titanium and non-metals such as pyrolytic carbon. Certain engineered plastics have also been found useful.
Another feature of rotors and stators suitable for application in the present invention is that they be capable of receiving and reliably retaining passive magnetic components which deliver forces stabilizing the rotor. Although not in the form of a mechanical surface-contacting bearing, the passive magnetic components utilized in the present invention may be positioned and/or arranged to function as magnetic thrust bearings. The rotor is also arranged to be capable of receiving and reliably retaining magnetic components such as electromagnetic components used in the drive system for delivering energy to the rotor for rotation. Preferably, an array of permanent magnets are positioned within the rotor and stator components in a brushless motor configuration. Alternatively, the drive mechanism may employ permanent magnet-to-permanent magnet couplings similarly mounted. The arrangement of the present invention provides for the economic utilization of a magnetically levitated rotor/stator assembly which may be fabricated by conventional processes, and therefore highly economically viable. Rotor stabilization and/or suspension may be achieved with passive magnetic bearings such as positioned in different arrangements or configurations. In preferred configurations, magnetically coupled bearings may provide positive forces in five of the six possible degrees of freedom, while providing one unstable negative force, preferably in a plane perpendicular to the axis of rotation, with this instability being overcome by a centrifugal force of greater magnitude.